The present invention relates to a portable thermal imaging camera, a device that is commonly used by firefighters and other rescue personnel to identify the seat of a fire from outside of a burning structure, to identify fire conditions within a burning structure hidden by heavy smoke, and/or to identify victims trapped within a burning structure.
Modern thermal imaging cameras, also referred to as thermal imagers, were introduced to firefighters in the mid-1990's. Originally developed for military applications, thermal imaging cameras quickly proved to be a valuable fire-fighting tool, essentially allowing firefighters to “see” in dark, smoke-filled and other extreme environments.
Thermal imaging cameras are now used by firefighters in numerous applications, including: to identify the seat of the fire from outside of a burning structure, thereby allowing the incident commander to determine what resources will be necessary and how to deploy such resources; to identify fire conditions and “hot spots” within a burning structure hidden by heavy smoke or building design features; and to identify victims trapped within a burning structure despite potentially blinding smoke conditions. Furthermore, thermal imaging cameras have been used to identify alternate egress routes for rapid and safe extraction of victims; to observe the impact of the water application on the heat and fire conditions; to identify areas within a burning structure with extremely high heat levels so such areas can be ventilated to reduce the chances of backdraft or flashover; to identify windows and doors in potentially blinding smoke conditions, thus allowing firefighters to rapidly vent a burning structure as they move through it; and to identify the movement of hazardous materials and identify product levels in containers within the burning structure.
Structurally, a portable thermal imaging camera includes several components that are contained in a housing designed to be carried by an individual, e.g., a firefighters First and foremost, the essential function of a thermal imaging camera is carried out by a sensor that reacts to thermal or infrared radiation, converting sensed thermal radiation (the “thermal picture”) of a scene into a set of temperature values, or thermal image data. One common sensor used in portable thermal imaging cameras is a focal plane array (“FPA”) type sensor, which has thousands of individual sensing elements. An example of a FPA type sensor is a microbolometer with a vanadium oxide (VOx) or an amorphous silicon sensing material.
A second component is a lens which focuses the infrared radiation from the scene onto the sensor. The quality of the lens is a major factor in the quality of the resultant thermal image data. One measure of quality is the f-number. A bigger lens means a smaller f-number and increased image quality. Of course, the size of the lens is limited by weight and costs considerations. For this reason, a common lens provides an f/stop of 1.0, and a common material for lens construction is germanium.
Another component is a thermal imaging engine, which processes the thermal image data to produce a thermal image. The thermal imaging engine may be a digital signal processor (DSP) or the equivalent. Generally, the thermal imaging engine will produce an image where hotter temperatures appear lighter, and cooler temperatures appear darker, such as with a grayscale imaging scheme. Additionally, the thermal imaging engine may provide “hot” colorization, where the hottest temperatures appear, progressively, in yellow, orange and red colors, and the cooler temperatures remain in the grayscale imaging scheme. For instance, “hot” colorization may be provided for temperatures above 500° F.
Yet another component is a display, the means by which the resultant thermal image is provided to the user. An active matrix liquid crystal display (“LCD”) is commonly used in portable thermal imaging cameras. The video display is commonly contained within the housing and viewable through a display window secured to the housing.
Again, each of the above-described components is contained within (or otherwise secured to) a common housing. The housing protects the delicate sensing components, and indeed protects such components in even severe fire conditions. At the same time, common housings are designed to facilitate transport. In this regard, some portable thermal imaging cameras are designed with a pistol grip that allows a firefighter to easily carry and aim the thermal imaging camera; others are provided with straps that allow the thermal imaging camera to be raised to the eyes much like binoculars.
In the early development of thermal imaging cameras, there was a limited dynamic range in that, when using the camera in an environment with extremely high temperatures, such as those encountered in a structure fire, the sensor would become saturated. As a result, it was difficult to identify fire conditions and “hot spots” in the thermal image with much precision. To overcome this problem, some thermal imaging cameras were provided with a user-operated mechanical iris that allowed for some regulation of the thermal energy reaching the sensor by changing the aperture of the lens. In other words, a user could artificially adjust the dynamic range (spread of temperatures) of the thermal image. This allowed the user to control the viewed image so that only “objects of interest” (the hottest items) showed up on the display.
Later advances in the sensors for thermal imaging cameras extended the dynamic range significantly, substantially eliminating the need for mechanical irises. However, a feature which allows the user to control the viewed image so that only objects of interest are highlighted on the display remains a desirable feature. More particularly, a selective temperature imaging feature that does not conflict with the normal “colorization” features of modem thermal imaging cameras is desired in firefighting overhaul and size-up operations. For instance, it is desired that such a selective temperature imaging feature allow a user to scan a large area, such as the inside of a department store, and automatically identify the hottest portion of the resultant image (e.g., an overheated light fixture) without knowing the location of the “hot spot” or its temperature. In order to prevent interference with the fixed “hot” colorization (yellow, orange, red) ranges, it is desired that the selective, or variable, temperature imaging feature highlight the hottest portion of the resultant image in an alternate colorization while the remaining portions of the image are displayed in a normal grayscale representation.